1. Technical Field
The present invention relates to electro-hydraulic forming to expand a tubular member in a die.
2. Background Art
In electro-hydraulic forming (“EHF”), an electric arc discharge is used to convert electrical energy to mechanical energy. A capacitor bank, or other source of stored charge, delivers a high current pulse across two electrodes that are submerged in a fluid, such as oil or water. Electric arc discharge vaporizes the surrounding fluid and creates shock waves. A workpiece that is in contact with the fluid may be deformed by the shock wave to fill an evacuated die.
Electro-hydraulic forming may be used, for example, to form a flat blank into a one-sided die. The use of EHF for a one-sided die may save tooling costs and may also facilitate forming parts into shapes that are difficult to form by conventional press forming or hydroforming techniques. Electro-hydraulic forming also facilitates forming high strength steel, aluminum and copper alloys. For example, advanced high strength steel (AHSS) and ultra high strength steel (UHSS) can be formed to a greater extent with electro-hydraulic forming techniques when compared to other conventional forming processes. Lightweight materials, such as AHSS and UHSS and high strength aluminum alloys are lightweight materials that are used to reduce the weight of vehicles.
The use of high strength, lightweight materials is increasing and has been proposed for hydroforming tubes. Tube hydroforming is a well-known technology that is currently used in production. One problem with conventional hydroforming of tubes is that increased pressure is required to fill sharp corners in local areas of the tube. The reduced formability of high strength steel and aluminum exacerbates the problems associated with forming sharp corners in localized areas of the parts when compared with forming such parts with mild steel. To form a tube having sharp corners, increased pressure is required in the hydroforming liquid that must be applied to all of the internal surfaces of the tube. To withstand the increased pressure, it is necessary to employ high tonnage presses and may require tens of thousands of pounds of pressure.
The above problems are addressed by Applicants' invention as summarized below.